Backers including Major League Baseball, the National Hockey League and Time Inc. plan to introduce their free digital network 120 Sports on Wednesday, an effort to compete for ad dollars against powers like ESPN and upstarts like Bleacher Report.

At the onset, 120 sports will run eight hours of original programming every day, from 6 p.m. through 2 a.m. Eastern Time, on apps and at its website 120Sports.com. Executives plan to roll out a two-hour block of morning programming soon, with the intention of growing into a 24-hour streaming network.

The viewing experience is somewhat frenetic. Original programming consists of 120-second blocks -- hence the network's name -- that air live but can also be viewed later. Hosts working in Oprah Winfrey's former studios in Chicago discuss sports news and trending topics, accompanied by highlights and clips from live games. Unlike TV anchors at ESPN, the hosts are not allowed to wear suits and ties.

The network "moves at the speed of Twitter," said Jason Coyle, president at 120 Sports.

ESPN remains the dominant media player in the sports world, both on TV and in digital media, where it drew 68 million unique visitors across mobile and desktop devices in May, up 42%, according to ComScore.

But 120 Sports' backers think their different approach can give them a grip.

"This is not something we built for the TV screen," said Bob Bowman, president and CEO at MLB Advanced Media, the interactive division of Major League Baseball. The network is built for a mobile experience that's meant to "resonate with this generation," he said.

MLB Advanced Media is managing the technology side of 120 Sports from its New York office. Beyond the MLB, the NHL and Time Inc., investors include Chicago-based digital media company Silver Chalice and Campus Insiders, the digital home for a number of college sports.

Investors contributed cash and services, according to Jason Coyle, president at 120 Sports. He declined to discuss the total cost of developing 120 Sports.

Todd Larsen, executive VP at Time Inc., said investments like 120 Sports are a "core part" of the strategy at Time Inc., which began trading publicly earlier this month and is looking for growth beyond its traditional magazine business.

But 120 Sports is also an effort by some of the major sports leagues to create a digital sports-media entity of their own, according to Mr. Coyle. "It's complementary to their core business," Mr. Coyle said.

120 Sports, for one thing, will help drive viewers to league and individual team websites and direct viewers to televised games. It backers also hope it will generate significant ad revenue.

Hosts including former ESPN anchor Michael Kim and former NFL player Bryant McFadden share the screen with "data cards," which are essentially boxes filled with content such as tweets, headlines from Time Inc.'s Sports Illustrated and other sources -- and ads.

During a preview of the network on Monday, a text-only ad for Verizon appeared in one of the data cards. Executives from 120 Sports said advertisers can include visual elements with their ads and update them in real time to reflect what's happening on the network. The ads can even adopt a native feel, execs said, blending seamlessly into the content on the screen.

Banners ads also appear in portions of the website. Brands will have the ability to sponsor specific sections as well, executives said.

Four companies have signed on as sponsors through 2014: Verizon, Geico, Nissan and Transamerica.

"With the sports media landscape so rapidly changing, it seemed like a great opportunity for a company like ours that's invested a lot in terms of digital engagement," said Bill Tate, senior VP of marketing at Transamerica, which worked with media agency Mindshare on the sponsorship.

He declined to say how much the company paid for the sponsorship.

"It requires us to think digital first," Mr. Tate added. "It's not the same old 30-second spot we'd use for March Madness."

A screen of trending topics.

Time Inc. and Silver Chalice are working together on ad sales, which are all direct, according to Mr. Larsen. Automated sales through programmatic technology might be available later on, he said.

The network will be promoted through digital ads on social media and Google AdWords, digital out-of-home ads in New York, a promotion on the left field wall at Chicago's U.S. Cellular Field (home of the White Sox) and pages in Sports Illustrated, according to Mr. Coyle. Time Inc. is also lending the network some of its promotional assets, such as its email lists, he added.

Mr. Coyle said that one year from now he hopes the network will be a "nearly ubiquitous brand" that is a "go-to part" of daily sports consumption.